Stirrer for rotary digester



y 21, 7 w. D. HARRISON STIRRER FOR ROTARY DIGESTER Filed May 12, 1954INVENTOR War! Dfi rrzsorz United States Patent 6 ce STIRRER FOR ROTARYDIGESTER Ward D. Harrison, Phillipsburg, N. J., assignor, by mesneassignments, to Riegel Paper Corporation, New York, N. Y., a corporationof Delaware Application May 12, 1954, Serial No. 429,283 3 Claims. (Cl.92-18) This invention relates to the production of pulp for papermaking, and more particularly to the cooking of a mass of raw materialwith a suitable liquor to form such pulp.

In making pulp, the raw material from which the fibers are to beobtained is mixed with a suitable liquor, the nature of which dependsupon the raw material, and the mixture is heated for a predeterminedperiod of time during which it is normally agitated to a certain extentto improve the chemical action of the liquor on the raw material. Duringcooking the lignins, dirt, etc., are removed from the raw material bythe liquor and subsequent to cooking the liquor is withdrawn from themixture and the pulp fibers delivered to a subsequent treatingoperation. I have found that this cooking operation, which is carriedout in a receptacle known as a digester, can be substantially improvedif the mixture of raw material and cooking liquor is handled in a mannernot heretofore employed. Hence I have found that a more uniformly bettercooked pulp with less shives, raw fibers and ligneous materials can beobtained, all other factors remaining the same, when the manner ofhandling the mixture of raw material and liquor proposed below isemployed rather than that which has heretofore been employed. Or in thealternative, I have found that by handling the mixture of raw materialand liquor in a digester in the manner I propose, a pulp of equal orperhaps slightly better quality can be obtained than has heretofore beenpossi ble while employing substantially less chemicals in the liquor,the pulp additionally being more uniformly cooked.

According to my invention, a mixture of the raw material from which thepulp is to be made and a suitable liquor therefor is placed in adigester and heated for cooking. Portions of the mixture of raw materialand liquor are then repeatedly moved from the lower part of the massthereof to an upper part of the mass with a substantial amount of theliquor of such portion being removed or withdrawn entirely from the massand returned thereto by spilling it over a substantial area onto the topof the mass. In this manner the mixing of the raw material and liquor isgreatly improved, with the raw material consequently being moreuniformly treated by the liquor, and conversely with the liquor beingemployed more efiiciently. Hence a considerable saving in the amount ofchemicals that must be necessarily employed in the liquor to accomplisha predetermined degree of cooking is elfected.

My invention also contemplates the PIOVlSlOl'l of a novel apparatus bywhich the above method of treating a mixture of raw material and liquormay be carried out.

For a better understanding of my invention, reference may be made to thefollowing more specific description thereof taken in connection with theaccompanying drawing in which one form of apparatus according to myinvention is illustrated and in which:

Fig. 1 is an elevation of said apparatus partly in section;

2,793,117 Patented May 21, 1957 Fig. 2 is a plan view in section takenalong line 2-2 of Fig. 1; and

Fig. 3 is a fragmentary elevation in section taken along line 3-3 ofFig. 1.

In the drawings there is illustrated a rotary digester 10 of the globetype having hollow trunnions 11 and 12 by which it is supported in fixedbearings 13 and 14. Through each hollow trunnion extends a steam pipe15, the inner ends of which extend to diametrically opposed positionsadjacent the inner face of the Wall of the digester 10. The digester maybe revolved by rotation of either of its trunnions by means not shown.Rotary steam joints permit the steam inlet pipes to rotate with thedigester. An opening is provided in the wall of the digester 10 adaptedto be sealed closed by a cover member 16. The raw material and liquormay be supplied to the digester and removed therefrom through thisopening. During operation of the digester, of course, cover member 16 istightly clamped in place to close the opening with a pressure tightseal. h

Within the digester, and preferably opposite the filling openingthereof, a rake indicated generally at 17 is mounted. The rake comprisesa plate 18 having an arcuate edge secured as by welding to the innerwall of the digester, thus forming a baffle. A flange 19 extendingsubstantially at right angles to the plane of plate 18 is secured to theinner edge of the plate throughout the extent thereof. A plurality offin plates 29 of varying sizes are secured on one side of plate 18 tothe plate and to the wall of the digester. These plates extendsubstantially at right angles to the plane of plate 18. A plurality ofplates 21 of varying sizes are secured to the wall of the digester onthe opposite side of plate 18. Each of plates 21 is additionally securedto a rod 22 which is in turn secured as by welding to plate 18. Plates21 and rods 22 extend a substantial distance beyond the inner edge ofplate 18 and are adapted to act as spaced tooth members in a mannersimilar to the teeth of .a conventional rake when the digester isrotated with a mass of pulp and liquor therein. Plates 21 also, as maybe seen in the drawings, extend substantially at right angles to theplane of plate 18.

In operation, the digester It) is filled about full with a mixture ofraw material and liquor. The cover 16 is then securely closed and thedigester rotated. Steam is forced into the digester through steam pipes15. In the particular digester shown steam is admitted alternatelythrough the two steam pipes when each is in the vicinity of the bottomof its path of travel, the steam being therefore projected upwardlythrough the mass of raw material and liquor. In order to obtain apredetermined temperature and pressure within the digester duringoperation, it has been found necessary, when the steam pressure hasrisen to about half that desired, to relieve non-condensible gas byclosing 013: the steam supply and blowing back or venting through thetrunnion to atmosphere employing for this purpose one steam pipe 15located during the period of this operation in the vapor area of thedigester. Admission of steam is then resumed and continued until theproper temperature and pressure has been reached. From this time on, thesteam is continually injected into the digester to maintain the desiredtemperature and pressure therein.

During rotation of the digester and cooking of the mass of raw materialand liquor therein, the rake 17 etfects thorough mixing of the liquorand raw material. The digester is rotated so that the rake will move inthe direction indicated by the arrow in Fig. 3. As the rake moves fromits lowermost position, as shown in Fig. 3, upwardly its plate 18 movesa portion of the mass of the mixture upwardly with it. As the rakeapproaches its horizontal position, some of the mass of raw material andliquor starts to spill therefrom. However, part thereof is maintained onthe plate by reason of flange 19 and carried further upwardly, and infact above the level of the mass within the digester. A good portion ofthis part is liquor which is then spilled over flange 19 as the rakeprogresses upwardly above the top of the mass. The last of the liquor,and of course some raw material mixed therewith, spills over the flange19 only after the rake has passed its uppermost position and has startedto descend.

The manner in which the rake shown agitates and mixes the mass of rawmaterial and liquor during rotation of the digester in the cookingthereof has, as previously indicated, resulted in a substantially moreuniform cooking and has enabled a substantial saving in the amount ofthe chemical components of the liquor necessary. The following clearlyillustrates this saving.

The above digester is presently being employed to cook rope. Thedigester is filled about full with a mixture of rope, water and causticsoda, the amount of each in the mixture being as follows: For each poundof rope there is employed 2 /2 to 3 /2 lbs. of water and .06 to .08 lb.of caustic soda. When necessary, emulsifying agents may be employed inappropriate amounts for degreasing, etc. Steam is injected until thepressure within the digester is from about 60 p. s. i. to about 100 p.s. i. The cooking operation is continued for about 9 hours, 2 to 3 hoursof this time being required to get the digester up to the desiredtemperature and pressure.

It has been found that the pulp obtained by the above operation is ofequal or better quality than that which has heretofore been obtainableonly with the use of .10 pound caustic soda per pound of rope. It hasalso been found that the resulting pulp is somewhat freer of shives, rawfiber and ligneous material.

Rag has also been effectively cooked in the above apparatus with asubstantial saving in the chemical content of the liquor and withincreased uniformity of the resulting pulp. I also contemplate that manymaterials which it has heretofore not been possible to satisfactorilycook in a rotary digester may now be efficiently and economicallytreated therein. Hence it is believed that such materials as corrugatedwaste, raw wood waste and raw kraft cook waste may now be satisfactorilyand economically treated.

Various changes and modifications in my method and apparatus asspecifically disclosed will of course occur to those skilled in the art,but it should be clearly understood that my invention contemplates suchchanges and modifications as are within the skill of the art Without adeparture from the scope thereof, and hence the invention should belimited only to the extent set forth in the appended claims.

I claim:

1. In a rotary digester for cooking a mixture of a raw material and asuitable liquor to form a pulp, a rake secured to the inner wall of thedigester and extending therein in a direction parallel to the axis ofrotation of the digester, said rake comprising a main plate disposed ina radial plane including the axis of rotation of the digester, a flangeextending along the inner edge of the main plate substantially at aright angle to the plane of said main plate, and a plurality of finplates secured to said main plate and lying in planes substantially atright angles to the planes of the main plate and flange.

2. A rotary digester as set forth in claim 1 in which some of the finplates are on one side of the main plate and others are on the otherside thereof, the fin plates on one side of said main plate extendinginwardly of said inner edge of said main plate.

3. In a rotary digester for cooking a mixture of a raw material and asuitable liquor to form a pulp, a rake secured to the inner wall of thedigester and extending therein in a direction parallel to the axis ofrotation of the digester, said rake comprising a main plate disposed ina radial plane including the axis of rotation of the digester, a flangeextending along the inner edge of the main plate substantially at rightangles to the plane of said main plate and a plurality of spaced toothmembers ex tending inwardly from said flange.

References Cited in the file of this patent UNITED STATES PATENTS827,617 Carritte July 31, 1906 1,142,521 Hornsey June 8, 1915 1,278,155Jefferson Sept. 10, 1918 1,638,886 Sherbondy Aug. 16, 1927 1,882,391Morterud Oct. 11, 1932 1,954,625 Hellstrom Apr. 10, 1934 2,185,408Kettenbach Jan. 2, 1940 FOREIGN PATENTS 1,020,080 France Nov. 12, 1952

1. IN A ROTARY DIGESTER FOR COOKING A MIXTURE OF A RAW MATERIAL AND ASUITABLE LIQUOR TO FORM A PULP, A RAKE SECURED TO THE INNER WALL OF THEDIGESTER AND EXTENDING THEREIN IN A DIRECTION PARALLEL TO THE AXIS OFROTATION OF THE DIGESTER, SAID RAKE COMPRISING A MAIN PLATE DISPOSED INA RADICAL PLANE INCLUDING THE AXIS OF ROTATION OF THE DIGESTER, A FLANGEEXTENDING ALONG THE INNER EDGE OF THE MAIN PLATE SUBSTANTIALLY AT ARIGHT ANGLE TO THE PLANE OF SAID MAIN PLATE, AND A PLURALITY OF FINPLATES SECURED TO SAID MAIN PLATE AND LYING IN PLANES SUBSTANTIALLY ATRIGHT ANGLES TO THE PLANES OF THE MAIN PLATE AND FLANGE.